APPENDIX 495 



CHAPTER XX 



Muscle fibers for microscopic examination may be obtained 

 from the leg of a frog, or even from the body of a recently 

 killed animal at the meat shop. Lay a small piece of muscle 

 in a drop of .75 per cent salt solution on a glass slide, and 

 with a pair of dissecting needles carefully pick the muscle to 

 pieces. Some of the smallest shreds, upon examination with a 

 one-fourth or a one-sixth inch objective, will be seen to be 

 single or grouped muscle fibers, which will show the striations 

 and the sarcolemma (Fig. 208). 



CHAPTER XXI 



Nerve fibers are readily obtained from the sciatic nerve in 

 the frog. This nerve may be found by removing the skin from 

 the back of a frog's thigh and carefully separating the under- 

 lying muscles. Among them will be seen the sciatic nerve, 

 covered in places with dark gray or black pigment spots. 

 Remove a quarter to a half inch of the nerve, being careful to 

 stretch it as little as possible ; lay it on the glass slide in a few 

 drops of .75 per cent salt solution ; cautiously tear it to pieces 

 in the direction of its length with dissecting needles ; then put 

 on a cover glass and examine under a high power. The nerve 

 will be found to consist of a number of nerve fibers, some of 

 which will show the primitive sheath (neurilemma), medullary 

 sheath, and axis cylinder (Figs. 210, 211). 



The relation between the stimulation of a nerve and the con- 

 traction of the muscle to which the nerve runs may be shown 

 as follows : Expose the sciatic nerve as directed above ; then 

 with the quick stroke of a sharp scalpel sever the upper end of 

 the nerve as near the body as possible. At the moment of do- 

 ing this the muscles of the leg and foot will probably contract. 

 Allow the nerve to rest for a few minutes ; then pinch its upper 

 end with a pair of forceps. Again the muscles will contract. 

 The stimulation may be repeated at intervals if the nerve be 

 allowed to rest for a few minutes between successive stimula- 



